Method of making glass clad energyconducting fibers



May 31, 1966 Original Filed Feb. 2. 1960 METHOD OF MAKING GLASS CLADENERGY-CONDUCTING FIBERS R. F, wooDcocK E'rAg.

l I l 22 8 INVENTQRS RICHARD F. WOODCOCK WILFRED P. BAZINETQJR.

ATTORNEY May 31, 1966 R. F. wooDcocK ETAL METHOD OF MAKING GLASS CLADENERGY-CONDUCTING FIBERS Original Filed Feb. 2. 1960 .3 Sheets-Sheet 2INVENTOF? RICHARD E WOODCOCK WILFRED P. BAZINET, JR.

ATTORNEY 3,253,896 METHOD F MAKING GLASS CLAD ENERGY- CONDUCTING FIBERSRichard F. Woodcock, South Woodstock, Coun., and Wilfred P. Bazinet,Jr., Webster, Mass., assignors to American Optical Company, Southbridge,Mass., a voluntary association of Massachusetts Original applicationFeb. 2, 1960, Ser. No. 6,136. Divided and this application Sept. 16,1963, Ser. No. 308,998

5 Claims. (Cl. 65-3) This is a division of application Serial No. 6,136filed February 2, 1960, and now abandoned.

This invention relates to improvements in light-conducting fibers andhas particular reference to devices formed therefrom and method ofmaking same.

While light-conducting fibers have been constructed of various differentmaterials, glass fibers, particularly those formed of optical glasses,have been generally considered to be the most desirable in themanufacture of light or image-transferring devices and it will becomeapparent hereinafter that this invention relates more particularly tothe making of glass light-conducting fibers and devices formedtherefrom.

[nited States Patent O If glass fibers are gathered into a compactorderly arl ray, they will transmit an image by breaking it up intoseparate components and these components are trans mitted independentlyfrom one end of the array to the other. However, when two glass fiberscome within a distance of `approximately a half wavelength of light ofeach other, some light will leak from one fiber to the next and therebycause a deterioration ofthe denition of the composite image.Consequently, it has been a practice to insulate one fiber from anotherby a relatively thin jacket of transparent material whose index ofrefraction is lower than that of the fiber.

Heretofore, devices embodying an intimate assembly of a plurality ofindividually insulated light-conducting fibers in side-by-side relationwith each other were fabricated by placing bonding materials such asepoxy resins or other suitable adhesives between the fibers to securethe fibers together and at the same time to fill in voids between theindividual fibers. In this,way, assemblies were made which were suitablefor certain limited uses. However, the above technique left much to bedesired since shrinkage and the effects of aging of the bondingmaterials often, after periods of storage or use, caused a weakening ofthe structure as well as distortion thereof and in one way or anothertended to eventually render the structures pervious to air and gases orotherwise unsuitable for use.

In view of the need for a more permanent and stronger structure whichwould be adaptable for use as a lightconducting face plate orlight-coupling device or the like on `pressurized or vacuumizedelectrontubes, for example, another technique involvedthe fusingtogether of the fibers by heating them at least to a temperaturesufficient to render the claddings thereof fusible. If the fibers arelightly fused, that is, only along their initially engaging edgeportions, little distortion of their cladding or general cross-sectionalshape results and no evident impairment of their light-transmittingproperties occurs. However, it is extremely diicult, and in most casespractically im possible when using relatively small fibers, to arrange agroup of such fibers in perfect interftting side-by-side relation witheach other regardless of their initial preselected cross-sectionalshapes. Therefore, voids between the individual fibers of the array areusually unavoidable unless, during the fusing operation, the fibers arecompacted by forces tending to distort their crosssectional shapes andthus literally squeeze them into compact inter fitting side-by-siderelation with each other.

Voids between the fibers of fused bundles are, more 3,253,896 PatentedMay 31, 1966 ICC often than not, objectionable, as mentioned above,particularly when the bundles are used in the fabrication of face platesfor use with pressurized or vacuumized articles wherein a secure,hermetically sealed structure is absolutely required. Thus, in instanceswhere such vacuumtight structures are needed, it has been necessaryheretofore to use structures in which the fibers were compacted underforce into more or less distorted interftting relation with each other.

In such cases, a distortion of the cross-sectional shape of the fiber asa whole and thinning of the individual fiber claddings at variouslocations along the length of the fibers often occurs with the resultthat at said locations, the light-conducting core parts of the fibersmay come i together within a distance such as to permit leakage of lightbetween the fibers.

It is well-known that distorted or irregularly shaped light-conductingbers have poorer light-transmitting properties than fibers of uniformcross-sectional shapes and dimensions. In fact, fibers which arecircular in cross-section have the best transmission properties mainlyfor the reason ,that the continuous uninterrupted cylindrical interfacebetween the core and cladding parts thereof provides means by whichsubstantially total internal reflection of all light rays enteringcircular fibers from all directions within the light-aperture angle ofthe fiber will take place throughout the length of the fiber. In fibershaving irregularly shaped interfaces, many light rays passingtherethrough strike the various points of interfacial irregularity atangles beyond the critical angle of reflection and thus are notinternally reflected but pass outwardly through the sides of the fibers.

In overcoming the difficulties and drawbacks of the abovediscussedprocedures relating to the fabrication of fiber optical devices, thepresent invention has for its principal object, the provision of noveland improved lightconducting fibers having means thereon by which saidfibers may be intimately and securely fused together in any desiredaligned relation with each other without distortion of theircross-sectional shapes and method of making such fibers and devicesformed therefrom.

Another object is to provide light-conducting fibers having doublecladdings thereon, one cladding being superimposed upon the otherwherein the innermost of said claddings is of such preselected index ofrefraction as to provide light-insulating means for said fiber and theoutermost 4of said claddings will serve as means to connect a pluralityof said fibers together when forming an assembly thereof.

Another object is to provide light-conducting fibers of the abovecharacter wherein said outer claddings are formed of materialpreselected to have a lower melting point than that of the remainingparts of the fibers so that a fused connection between each of a groupof such fibers can be made without causing distortion of the core andinner cladding parts of said fibers.

Another object is to form said outermost claddings as well as the otherparts of said fibers of glass material whereby, when an assembly of saidfibers is made a composite glass structure will result having extremerigidity and permanency.

Another object is to provide light-conducting fibers with doublecladdings of the above character wherein said outer cladding on each ofsaid fibers is of sufficient volume in accordance with thecross-sectional size of the core and inner cladding parts of said fibersas to completely fill in all voids between said fibers when a pluralitythereof are intimately grouped together and heated light-transferringglass structure which embodies a plurality of individuallylight-insulated light-conducting fibers permanently secured together inside-by-side relation with each other.

Another object is to provide means and method of making a structure ofthe above character completely of glass material without causingdistortion of the initial cross-sectional configuration of the core andinner cladding parts of the fibers or in any way deterring the originallight-transmitting properties of said fibers.

Another object is to provide novel means and method of making a secureand permanently vacuum-tight face plate embodying a plurality ofsubstantially undistorted light-conducting fibers of circularcross-section disposed in adjacent side-by-side relation with eachother.

Other objects and advantages of the invention will become apparent fromthe following description when taken in conjunction with theaccompanying drawings in which:

FIG. l is a greatly enlarged longitudinal cross-sectional view of alight-conducting fiber of the type embodying the invention;

FIG. 2 diagrammatically illustrates a method of forming a glass assemblyfrom which light-conducting fibers such as illustrated in FIG. 1 aresubsequently drawn;

FIG. 3 is a diagrammatic illustration of'a'n alternate method by which asimilar glass assembly may be formed;

- FIG. 4 is a side elevational view partly in cross-section of a glassassembly resulting from the practice of onev or the other of thetechniques illustrated by FIGS. l and 2;

FIG. 5 is a diagrammatic illustration of means for forming alight-conducting fiber from an assembly such as shown in FIG. 4;

FIG. 6 is a diagrammatic illustration of a preferred method of forming alight-transferring device from a plurality of fibers of the above type;

FIG. 7 is an enlarged fragmentary transverse crosssectional view takenapproximately on line 7--7 of FIG. 6;

FIG. 8 is a view similar to FIG. 7 illustrating a modified form of theinvention;

FIGS. 9 and 10 illustrate the forming of a light-transferring plate froma composite fused assembly of fibers of the above character; and l FIG.11 illustrates the building of an enlarged face plate or the like from aplurality of smaller light-transferring plates such as shown in FIG. 10.

Referring more particularly to the drawings, it will be seen that theinvention relates to the fabrication of doubly clad light-conductingfibers, such as shown in FIG. l, and devices formed therefrom, such asshown in FIGS. 6-10, for example. The light-conducting fibers 20 of theinvention (see FIG. 1) each embody, in their finished state, a core 21of an optical glass having a relatively high index of refraction, afirst or inner relatively thin cladding 22 surrounding said core 21 of arelatively low index of refraction and a second or outer cladding 23 ofa glass material having a lower melting point than that of the aboveglasses and of a precontrolled thickness such as will be discussedhereinafter. The core 21 and inner cladding. 22 parts of each of thefibers together serve as a light-conducting element adapted to transferlight by internal reflection through the fiber and the outermostcladding 23 basically serves as a glass flux adapted to ultimately forma matrix by means of which a plurality of fibers 20 may be joinedtogether without distorting the initial cross-sectional shape of thecore and inner claddings parts or in any way deterring thelight-transmitting properties of the fibers.

The core 21 and inner cladding 22 parts of the fiber 20 are formed ofglasses having indices of refraction so preselected as to provide thefiber 20 with a desired aperture or light-acceptance angle. Theselection of glasses is made in the usual manner from-the formula sin a4 equalling the square root of :L12-nf wherein ,t is the maximumaperture angle (see FIG. l), n, is the index of refraction of the coreand n2 is the index of refraction of the cladding. As an example, anoptical flint glass having an index of refraction of 1.75 might be usedfor the forming of the core 21 and a soda-lime glass or the like havingan index of refraction of approximately 1.52 might be used in formingthe inner cladding 22 giving the fiber in aperture angle fr ofapproximately 60.

The outer cladding 23 is preferably formed of a glass or inorganicvitreous material preferably having a lower melting point thantheglasses of the core and cladding parts 21 and 22 respectively forreasons which will become readily apparent hereinafter. For certainapplications of use, it might be preferable to form the outer cladding23 of a glass material having a certain preselected index of refractionand/or a specific color to provide light-absorbing means between a groupof bundled bers. However, when the outer cladding 23 is used solely asmeans to join a group of fibers together, as will be describedhereinafter, its index of refraction is inconsequential. For most uses,lead containing glasses or commercially available powdered solder glassor the socalled glass enamels are preferred for use in forming outercladdings 23 of fibers 20.

In` making a doubly clad fiber 20, a relatively large cylindrical glassassembly 24 (see FIG. 4) is initially formed and the liber 20 issubsequently drawn from the assembly 24. One -method of constructing anassembly 24 is illustrated diagrammatically in FIG. 2 wherein auniformly dimensioned solid rod 25 of a preselected optical glass,having an index of refraction of that desired of the core part 21 of thefiber 20 is placed within a sleeve or tube 26 of glass of the index ofrefraction desired. of the inner cladding Z2 of the liber 20. The wallthickness of the tube 2-6 is selected in accordance with thecross-sectional size of the rod 25 so as to cause the rod and tubeassembly to be substantially equal, proportionately, to the ultimaterelative core 21 to cladding 22 sizes desired of the fiber 20. The outerside surface of the tube 26 is completely coated with glasslike material27 such as a commercial glass enamel or any powdered glass material orinorganic vitreous material having a lower melting temperature than thatof the tube 26.

A preferred method of applying the coating 27 is to mix the powderedglass with water, pine oil or any suitable vehicle which is volatile orwill burn off under temperatures` which are used subsequently to firethe coating and secure it to the tube 26, as will be describedpresently. Atter having formed a paste-like mixture of glass powder, itis applied to the tube 26 with a brush 28, as shown (FIG. 2) or bydipping the tube 26 into the mixture while taking care to prevent themixture from entering internally of the tube. Alternatively, the tube 26may be rolled over a layer of the paste-like mixture, if desired. In anycase, the coating 27 is controlled to be of a substantially uniformthickness in accordance with the amount of material needed to providesecuring means for the fibers when making an assembly thereof, as willbe described in more detail hereinafter.

With the paste-like coating of powdered glass thus applied to the tube26, the tube 26, with or without the rod 25 therein, is placed in aconventional lheating chamber, not shown, and fired -by heating the samet0 a temperature of approximately 1050 F. for a time period ofapproximately one hour. The exact temperatures and time cycles fortiring will, of course, vary somewhat for different types of glasspowders which might be used. This fuses the coating 27 to the tube 26and forms a contiguous glass cladding over the tube 26 to produce anassembly, such as shown in FIG. 4, when the rod 25 is within the tube26.

Another method of preparing an assembly, such as shown in FIG. 4, isshown diagrammatically in FIG. 3 where, again, a rod 29 and tube 30similar to the rod and tube 26 are assembled by placing the rod 29within the tube 30. In the present case, however, a second sleeve ortube 31 of low melting leadcontaining glass or the like is fitted overthe tube 30 to eventually become the outermost cladding 23 of the fiber20 when the composite assembly of the rod 29 and tubes 30 and 31 aresubsequently drawn to fiber size. The tube 31 is preselected to have awall thickness proportionately controlled in accordance with the nalthickness desired of the outer cladding 23 of the fiber 20 4and isformed of a material having a lower melting temperature than the tube 30and rod 29 combination.

By either of the two above-described methods, an assembly 24, such asshown in FIG. 4, can be formed wherein a core section 32 is surroundedby an inner cladding 33 having an outer cladding or tube 34, as the casemay be, of glass material thereon. It is pointed out that the outercladding 34 should have a melting point of from 50-100 F. lower thanthat of the inner cladding when both are at approximately the sameconditions of fiber drawing viscosity.

After having `formed a glass assembly 24 by one or the other of thetechniques shown in FIGS. l and 2, the assembly 24 is heated to afibemirawing viscosity adiacent one of` its ends and drawn to fiber sizepreferably with means such as shown diagrammatically in FIG. 5. While itis obvious that a ber 20 may be drawn from an assembly such as 24 byhand or with many variations of the apparatus herein disclosed, it willbe apparent that in order to produce a superior fiber 2|) of uniformcross-sectional size throughout its length, the fiber should be drawn ata continuous uniform precontrolled rate in accordance with the sizedesired of the fiber while the assembly 24 is lowered substantially inthe direction of drawing continuously at a uniform slower rate alsocontrolled in accordance with the size desired of the fiber.

The apparatus of FIG. 5, which is shown for purposes of illustration,embodies a base 35 having a vertically extending column 36 thereonfastened at one end 37 to the base 35 and at its opposite end 38 to theceiling 39 of a room in which the apparatus is used. Alternatively, theend 38 of the column 36 may be supported from the base 35 with suitablebrackets or the like, not shown, if it is so desired. A slide 40 ismounted on the column 36 with suitable conventional bushing `means 41 soas to permit the slide 40 to be movable along and guided by the column36 by means of a rotatable lead screw 42 passing through an extension ofthe slide 40 in which the screw 42 is threadedly engaged. The lead screw42 is supported in parallel relation with the column 36 by a socket-likeconnection 44 fastened to the ceiling 39 and bearing means 45 in thebase 35. The slide 40 is moved along the column 36 by operation of adrive motor 46 which, by means of a belt and pulley arrangement 47,andconventional speed-reduction gearing within a gear box 48 along withinterconnecting gears 49 between the reduction gearing and the leadscrew 42, causes rotation of the lead screw 42. At the end of the slide40 opposite to its connection with the lead screw 42, there is provideda clamp 50 in which one end of the glass assembly 24 is secured, asshown, and a vacuum line 51 from a conventional vacuum pump or the like,not shown, is provided to evacuate air or gases from between parts ofthe glass assembly during the fiber drawing operation. As showndiagrammatically, communication between one end of the assembly 24 andthe vacuum line is made through openings 52 in the slide 40.

On the column 36, between the slide 40 and the base 35, there isprovided a shelf-like bracket 53 having an opening 54 therethrough insubstantially coaxial alignment with the glass assembly 24. The bracket53 is clamped to the column with screws or the like 55 and providesmeans upon which a ring-like glass heating furnace 56 is supported. Thefurnace 56 may be of any wellknown design preferably embodying aring-like electrical heating element in approximately coaxial alignmentwith the opening 54 by means of which the material of the glass assembly24 can be heated to a fiber-drawing viscosity when passed axiallytherethrough, as illustrated.

In operation, the slide 40 is initially positioned adjacent theuppermost end 38 of the column 36, substantially as shown, and the glassassembly 24 is clamped in place and lowered endwise into the furnace 56by operation of the lead screw 42. It is pointed out that previous tothe positioning of the assembly 24 in the apparatus, its end which is tobe lowered into the furnace 56 is preferably heat-sealed to prevent thecore and/or inner tubular parts of the assembly from slipping out ofplace before said parts are fused together by the heat of the furnace56. The sealing of said end of the assembly also permits immediateevacuation of air from within the assembly through the vacuum line 51.

With the glass assembly 24 lowered into the furnace 56, as shown, thefiber 20 is drawn by gripping the depending end of the assembly andpulling the molten material thereof longitudinally away from theassembly at a rate controlled in accordance with the cross-sectionalsize desired of the fiber while simultaneously continually lowering theslide 40 to feed the assembly endwise into the furnace at a ratecontrolled in accordance with the rate of removal of the material of theassembly 24 resulting from the drawing of the fiber 20 therefrom.

The drawing of the fiber 20 may be started by simply placing a solidglass rod upwardly and endwise against the initially depending end ofthe assembly 24 to cause the glass rod to fuse to the glass assembly 24.When the glass rod has become well fused, it is drawn downwardly awayfrom the assembly 24 pulling the material of the assembly` 24 along withit thereby forming the fiber 20. The fiber is then broken away or cutfrom the glass rod and attached to drawing means such as the rotatabledrum 58 shown in FIG. 5. The drum 58, which is supported on the base 35by a shaft 59, is driven by the motor 46 through gearing in the gear box48 at a predetermined speed of rotation in accordance with the selectionof gears in the box 48 by which the shaft is rotated. It is pointed outthat the relative rates of rotation of the lead screw 42 and drum 58 areprecontrolled by the selection of lproper gearing ratios within the box4S. It should also be understood that the particular drive means for thelead screw 42 and drum 58 which has been shown in FIG. 5 is purelydiagrammatic and has been given for purposes of illustration only.

When the fiber 20 is drawn from the assembly 24, as described above, itsrelative proportions as to core and cladding sizes will remainsubstantially the same as the relative core to cladding sizes of theinitial assembly 24 regardless of the minute size of only a few micronsin diameter to which the liber may be drawn. Furthermore, the fiber willretain substantially the same cross-sectional shape as that of theassembly 24.

In producing a fiber from an assembly 24 which was fabricated by themethod illustrated in FIG. 2 wherein, for example, a rod 22 of opticalflint glass having an index of refraction of approximately 1.75 and asleeve or tube 26 of soda-lime glass coated with a glass powder or othersimilar inorganic vitreous material are used, the assembly would beheated to approximately 1500 F.1600 F. for yfiber-drawing purposes.

However, with an assembly 24 which was formed of a rod 29 of optical intglass having an index of refraction of approximately 1.75 within asleeve or tube 30 of sodalime glass, both placed within an outer sleeveor tube 31 of a lead-containing glass having a melting temperature ofapproximately 50 F.-100 F. lower than that of the soda-lime glass whenboth are approximately at the same conditions of viscosity, saidassembly would be heated to approximately 16401680 F. for fiber-drawingpurposes.

In all cases, the resultant fiber 20 will have the innerlight-insulating cladding 22 (see FIG. l) and the outer cladding 23,described hereinabove, by means of which a plurality of such fibers maybe joined in fused intimate relation with each other without causingdistortion of the core 21 and inner cladding parts 22 of the fibers.

A preferred method of forming a composite light-conducting device inaccordance with this invention, from a plurality of doubly clad fibers20, is to place a great num- 'ber of said fibers longitudinally in arelatively large diameter, thin walled glass tube 60 such as shown inFIG. 6. The fibers 20 are preferably packed rather tightly in the tube60 after having been bundled together and aligned in substantiallyparallel relation with each other by any known technique. Successfulpacking and pre-aligning of a bundle of fibers each of relatively smalldiameter has been accomplished by dipping the fibers in a liquid such asalcohol and withdrawing the same endwise from the liquid one or moretimes.

After having placed the fibers 20 in the tube 60 which is formed of aglass having a melting temperature within the range of that of theoutermost coating glasses of the fibers themselves, the completeassembly is lowered gradually endwise through a heating chamber 61 and avacuum is drawn at the uppermost end of the tube 60 to evacuate air and/or other gases from between the fibers 20 while simultaneously causingthe tube 60 to collapse tightly around the fibers and force them intoside-by-side engaging relation with each other, as shown by themagnitied cross-sectional view of FIG. 7. The temperature used for theabove collapsing operation for fibers 20 formed of the above-discussedcombinations of glasses would be approximately between 1200 and 1300" F.In order to further assist in the compacting of the fibers 20 and toassure a complete air-tight seal between the fibers, it has been foundthat a slight pull or endwise drawing of the assembly of FIG. 6 as it islowered through the heating element 61 produces excellent results.

Referring more particularly to FIG. 7, it will be seen that the netresult of the above process is that of forming a composite integrallyfused glass structure wherein the complete area between `the individualcore 21 and finst cladding parts 22 of the fibers 20 is completelyfilled solidly with the glass material of the outermost claddings 23thereof without causing distortion of the said core and first claddingparts of the fibers. In this way, round fibers 20 which, as discussedabove, have superior lighttransmitting properties, may be used to formlight-conducting devices of the character shown in FIGS. 6 and 7.

From'the above, it should be evident that control of the initialthickness of the outermost cladding 23 of the fibers will determine theproximity of the combined core 21 and first or inner cladding 22 partsof the fibers 20 in the nal assembly of FIGS. 6 and 7. That is, bypropercontrol of the thickness of the outer cladding 23 which ultimatelybecomes the glass matrix between the fibers, the fibers can be nestedtogether in engaging side-by-side relation with each other, as shown inFIG. 7. Nevertheless, if it is desired to form an assembly such as shownin FIG. 8 wherein the core 21 and first or inner cladding parts 22 ofthe fibers are spaced from each other for special applications of use, athicker outer cladding 23 on the initially formed fibers 20 and propercontrol of fusing temperature and time cycle will produce this result.

It is pointed out that assemblies of fibers 20, such as shown in FIGS. 6and 7, may be made by other obvious methods or by a technique embodyingthe subject matter articles such as cathode ray tubes, for example,wherein such face plates must be sufficiently rigid to avoid collapseunder atmospheric or other pressures as well as being impervious to airor gases and resistant to chemical attack by certain gases oratmospheres within the tubes or the like.

In forming a face plate from an elongated assembly, such as shown inFIGS. 6, 7 and 8, the said assembly is vsimply cut, as shown in FIG. 9,in a direction normal to the axes of the fibers 20 and to a thicknessapproximately that desired of the face plate 62 to be formed therefrom.Thereafter, one or both sides of the plate 62 are optically ground andpolished to render the cut ends of the fibers 20 highly receptive tolight entering or leaving the same.

The face plate 62 may be used as is, with the outer surrounding glasstube 60, or cut along the dot-dash lines 63 of FIG. l0 to a square,hexagonal or any shape desired. This removes the glass tubular part 60.

By cutting the face plate 62, as shown in FIG. l0, several such elements64, see FIG. ll, may be edge-fused or otherwise secured together to formenlarged face plates. In all cases, the resolution which can be expectedwhen face plates of the above character are used to transfer opticalimages is dependent upon the fineness of the individual fiber 20 sizeswhich can be controlled, as described above in the initial fiber-drawingoperation of FIG. 5, or by grouping a plurality of fibers, as shown inFIG. 6, with out the tube 60 and redrawing said grouping to reduce thefiber element size thereof before proceeding with the steps illustratedby FIGS. 6-l l.

From the foregoing, it will be seen that efficient and economical meansand method have been provided for accomplishing all of the objects andadvantages of the invention. Nevertheless, it is apparent that manychanges in the details of construction, arrangement of parts or steps invthe process may be made without departing from the spirit of theinvention as expressed in the accompanying claims and the invention isnot to be limited to the exact matters shown and described as only thepreferred matters have been given by way of illustration.

We claim:

1. The method of making glass clad energy-conducting fibers for use aslong and thin individually insulated energy-conducting guides in devicesformed of fused bundles thereof, each fiberhaving a glass claddingadapted to serve as an insulating medium for preventing energy beingconducted through the fiber from passing outwardly through the sidesthereof and an outer layer of glass on said cladding adapted to serve asa medium for connecting the fibers together in such devices, said methodcomprising the steps of placing a rod of energyconducting materialwithin a tube formed of said glass cladding material, surrounding saidtube with a layer of glass having a substantially lower meltingtemperature than the glass of said tube, heating the combination to atemperature sufficient to render all parts thereof fusible to each otherand capable of being drawn as a unit, drawing from one end of the heatedcombination a long and thin unitary strand having the cross-sectionalsize desired of said fibers and vthe bers together in such devices, saidmethod comprising the steps of placing a rod of energy-conductingmaterial within a tube formed of said glass cladding material,surrounding said tube with a substantial thickness of powdered glasshaving a substantially lower melting temperature than the glass of saidtube and causing said powdered glass to become fused to said tube duringone lstrand having the cross-sectional sizel desired of said fibers andcutting said strand transversely at a number of spaced points therealongto form said fibers.

3. The method of making an energyconducting device .comprising thestepsof providing a number of long and thin individually glass cladenergy-conducting elements comprising the steps of providing a number oflong and thin fibers each having a core of energy-conducting materialsurrounded by a cladding of glass having approximately the same meltingtemperature as said core and an outer surrounding layer of glass on saidcladding having a substantially lower melting temperature than saidcladding glass, said core, cladding and layer of glass all being fusedtogether as an integral unit, bundling said fibers together inside-by-side relationship with each other and heating said bundle to atemperature suflic'ien't to cause said outer layers of glass to melt andfuse together as an v integral connecting medium between said fibers.

4. The method as recited in claim 3 wherein said bundle is heated to atemperature below the melting temperature of said Core and claddingmaterials of said fibers to prevent deformation thereof during fusion ofsaid outer layers of glass.

5. The method of making an energy-conducting device comprised of aunitary bundle of fused together long and thin individually glass cladenergy-conducting bers each having a glass cladding adapted to serve asan insulating medium for preventing energy being con'ducted through thefibers from passing outwardly through the sides thereof and an outerlayer of glass on said cladding adapted to serve as a medium forconnecting the fibers together in said device, said method comprisingthe steps of placing a rod of energy-conducting material within a tubeof glass cladding material, surrounding said tube with a layer of glasshaving a substantially lower melting temperature than the glass of saidtube, heating the combination sufficiently to render all parts thereoffusible to each other and capable of being drawn as a unit, drawing fromone end of the heated combination a long and thin unitary strand havingthe cross-sectional size desired of said fibers and cutting said strandtransversely at a number of spaced points therealong to form saidfibers, bundling said fibers together in sidcbyside relationship witheach other and heating the bundle to a temperature sutiicient to causesaid outer layers of glass to melt and fuse together as an integralconnecting medium between said fibers.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCESNature: No. 4392, Jan. 2, 1954, p. 39, article entitled, A New Method ofTransporting Optical Images Without Aberrations.

DONALL H. SYLVESTER, Primary Examiner. F. W. MIGA, A ssstant Examiner.

1. THE METHOD OF MAKING GLASS CLAD ENERGY-CONDUCTING FIBERS FOR USE ASLONG AND THIN INDIVIDUALLY INSULATED ENERGY-CONDUCTING GUIDES IN DEVICESFORMED OF FUSED BUNDLES THEREOF, EACH FIBER HAVING A GLASS CLADDINGADAPTED TO SERVE AS AN INSULATING MEDIUM FOR PREVENTING ENERGY BEINGCONDUCTED THROUGH THE FIBER FRO PASSING OUTWARDLY THROUGH THE SIDESTHEREOF AND AN OUTER LAYER OF GLASS ON SAID CLADDING ADAPTED TO SERVE ASA MEDIUM FOR CONNECTING THE FIBERS TOGETHER IN SUCH DEVICES, SAID METHODCOMPRISING THE STEPS OF PLACING A ROD OF ENERGY-CONDUCTING MATERIALWITHIN A TUBE FORMED OF SAID GLASS CLADDING MATERIAL, SURROUNDING SAIDTUBE WITH A LAYER OF GALSS HAVING A SUBSTANTIALLY LOWER MELTINGTEMPERATURE THAN THE GLASS OF SAID TUBE, HEATING THE COMBINATION TO ATEMPERATURE SUFFICIENT TO RENDER ALL PARTS THEREOF FUSIBLE TO EACH OTHERAND CAPABLE OF BEING DRAWN AS A UNIT, DRAWING FROM ONE END OF THE HEATEDCOMBINATION A LONG AND THIN UNITARY STRAND HAVING THE CROSS-SECTIONALSIZE DESIRED OF SAID FIBERS AND CUTTING SAID STRAND TRANSVERSELY AT ANUMBER OF SPACED POINTS THEREALONG TO FORM SAID FIBERS.